1. Technical Field
Aspects of this document relate generally to telecommunication systems and techniques for transmitting data across a telecommunication channel.
2. Background Art
In all forms of communications, the objective is to develop smaller antennas that provide higher performance while occupying less space. The natural result of using a smaller antenna is that the beam patterns become wider as the antennas necessitate a less sharply focused signal transmission and the result is energy being received in undesirable locations. The options to mitigate the problem of off-axis emissions are as follows: 1) use a larger antenna, which may not be an option due to space requirements; 2) lower the transmitted power resulting in less overall power being used for the transmission link; or 3) using a combination of decreasing the power while using signal processing techniques such as Forward Error Correction (FEC) or spread spectrum to mitigate the effects of the reduced transmission power or smaller antenna. In the art, the amount of power per unit bandwidth (e.g. Watts/Hz or dBW/Hz) is known as the Power Spectral Density (PSD). For a given amount of power, a smaller antenna emits the power over a wider area, resulting in higher off axis emissions. Conversely, a larger antenna emits the same amount of power with lower off axis emissions.
For example, in satellite communications, as the size of the antenna is reduced, a resulting and negative aspect of the reduction to the size of the antenna aperture is that off-axis emissions increase, resulting in less energy being directed into the bore sight to the intended target receiver or satellite and more energy ending up in the off-axis (not into the bore sight).
Therefore, a need exists for a method and system that addresses communications on the move (COTM) or satellite on the move (SOTM) products in which the antennas are small (small aperture size), resulting in higher adjacent satellite interference (ASI) conditions being experienced due to the wider transmission beam from the antenna. The result is that the PSD may be higher than can be tolerated on the adjacent satellites (off axis emissions).
Development of a method and system that allow a transmission device to operate at an established transmission configuration, but keep the spectral allocation as a constant value (e.g. remaining within the 3 dB bandwidth) is advantageous. Many devices in the art suffer from problems when changing the transmission carrier signal characteristics that result in the symbol rate having to be adjusted. Therefore, a need exists for a method and system that allow a transmission carrier signal's spectral allocation to remain at or near a desired (e.g. 3 dB) bandwidth, but use spread spectrum techniques, namely Direct Sequence Spread Spectrum (DSSS) to effectively lower the PSD by while holding the spectral allocation as a constant value during operation.